1. Field of the Invention
The present invention relates to a switch for a vehicle, which is mainly used to control the on-off operation of a stop lamp in response to the operation of the brake pedal of an automobile.
2. Background Art
In recent years, press-type switches for vehicles have been increasingly used to control a stop lamp that lights when the brake pedal is depressed and goes out when released.
Such a conventional switch for a vehicle is described with reference to FIG. 5.
FIG. 5 is a sectional view of a conventional switch for a vehicle. The switch includes substantially box-shaped, open-top case 1 made of insulating resin, and operating body 2 also made of insulating resin. Case 1 has a plurality of fixed contacts 3 embedded therein, with terminal parts 3A of fixed contacts 3 being protruded from the bottom surface of case 1.
The switch further includes pressure-contact spring 5, which brings movable contact 4 made of a conductive metal into elastic contact with fixed contacts 3 from below, so that fixed contacts 3 are electrically connected to each other via movable contact 4, thereby forming a switch contact. Pressure-contact spring 5 is held in a slightly compressed condition between the bottom surface of case 1 and movable contact 4.
The switch further includes coiled return spring 6 in a slightly compressed condition between the bottom surface of operating body 2 and the bottom surface of case 1 so as to bias operating body 2 upward.
The switch further includes cover 7, which covers the open top of case 1 and has hollow cylindrical part 7A protruding upward. Operating body 2 has operating shaft 2A, which moves up and down in hollow cylindrical part 7A. The top end of operating shaft 2A is protruded upward from hollow cylindrical part 7A.
The switch for a vehicle thus structured is generally installed just before the brake pedal of an automobile, with operating shaft 2A of operating body 2 pressed by an arm or the like, and with terminal parts 3A of fixed contacts 3 connected to the power supply and the stop lamp via connectors or the like.
More specifically, when the brake pedal is not depressed, operating shaft 2A of operating body 2 is pressed downward so as to compress pressure-contact spring 5 and return spring 6, thereby moving movable contact 4 downward away from fixed contacts 3. In this condition, fixed contacts 3 are electrically disconnected from each other, and therefore, the stop lamp is out.
When the brake pedal is depressed, on the other hand, the arm leaves operating shaft 2A to remove the pressure, allowing the elastic restoring force of return spring 6 to move operating body 2 upward. Movable contact 4 is also pressed by pressure-contact spring 5 so as to come into elastic contact with fixed contacts 3. As a result, fixed contacts 3 are electrically connected to each other so as to connect the stop lamp to the power supply, thereby illuminating the stop lamp.
The switch for a vehicle is installed near the brake pedal of the automobile exposed to a comparatively high level of dust, gas, moisture, and the like. Furthermore, the arm or the like to press operating shaft 2A of operating body 2 is generally coated with a lubricant or the like. Therefore, the lubricant, gas, dust, moisture, and the like may enter the inside of the switch for a vehicle from operating, shaft 2A, hollow cylindrical part 7A, or the gap between case 1 and cover 7.
The switch contact of the switch for a vehicle has the aforementioned structure in which pressure-contact spring 5 allows movable contact 4 to move up and down so as to come into contact or to separate from fixed contacts 3 arranged opposite to movable contact 4. The lubricant, gas, dust, moisture, and the like entered the inside of the switch may adhere to fixed contacts 3 or movable contact 4 so as to generate carbides or silicides on their surfaces. The generation of these compounds may disrupt the electrical contact and separation between the contacts.
In an attempt to prevent the adherence of the lubricant, gas, dust, moisture, and the like to the surfaces of the contacts, the switch for a vehicle is generally sealed, for example, by covering operating shaft 2A or hollow cylindrical part 7A with a rubber cap or by applying an adhesive agent or a shielding material to the gap between case 1 and cover 7.
One such conventional device is disclosed in Japanese Patent Unexamined Publication No. 2003-151398.
The conventional switch for a vehicle, however, is required to have a sealed structure to achieve stable electrical contact and separation between the contacts. This causes an increase not only in the number of components but also in the time required for the assembly of the switch.